Heat a pan over medium-high heat. Sauté bacon until just beginning to brown. Add sliced shallots and continue to cook until shallots have softened.
Deglaze the pan with balsamic vinegar, scraping up the brown bits, then quickly add brown sugar. Allow the brown sugar to dissolve and the liquid to thicken to a light syrup.
Remove from heat and purée in a blender or food processor until smooth. Refrigerate until ready to use.

Yield: 1 cup